Method for passivating tantalum metal surface and apparatus thereof

ABSTRACT

A method for passivating tantalum metal surface is provided, the method comprises cooling tantalum metal to or below 32° C. and/or passivating tantalum metal surface by oxygen-containing gas with a temperature of 0° C. or below. Also provided is an apparatus for passivating tantalum metal surface for applying the method, comprising a heat treatment furnace, an argon forced-cooling device and/or a device for cooling oxygen-containing gas.

TECHNICAL FIELD

Present invention relates to the field of tantalum metal production, and particularly to a method and apparatus for producing tantalum powder or porous tantalum metal for electrolytic capacitor.

BACKGROUND ART

Tantalum metal is mainly used for manufacturing tantalum electrolytic capacitors. However, the manufacturing process of tantalum electrolytic capacitors usually comprises compacting tantalum powder into a compact, sintering the compact in a vacuum furnace into a porous body in which the particles are interconnected, subjecting the porous agglomerate to anodic oxidization in a suitable electrolyte to form homogeneous interconnected dielectric oxide film on the surface of the porous particles, i.e. form an anode, coating a cationic material on the surface of the oxide film, and then packaging and forming the anode and the cathode of an capacitor. The parameters used for evaluating tantalum electrolytic capacitors mainly include capacitance, DC (direct current leakage) and equivalent series resistance (ESR). Development tendency in capacitors is to have high capacitance, low leakage current and low equivalent series resistance (low tgδ for anode). The amount of impurities in capacitor level tantalum powder, which is the main feedstock of tantalum electrolytic capacitors, particularly oxygen amount, has a great effect on the leakage current. Low leakage current requires the tantalum powder to have low oxygen content.

Generally, tantalum powders for electrolytic capacitors should subject to heat treatment, for the purpose of purifying tantalum powders on the one hand, and condensing tantalum microparticles into porous particles on the other hand, so as to improve the physical properties of tantalum powders, such as flowability of tantalum powders, and thus improve the properties of the electrolytic capacitors manufactured therefrom, such as the capacitance, leakage current and equivalent series resistance (ESR) of the capacitors. U.S. Pat. No. 3,473,915 discloses a heat treatment of tantalum powders, comprising heat condensing 2-30 μm of tantalum powders at 1200° C.-1500° C. under inactive atmosphere to form multi-junction porous particles to thereby obtain condensed tantalum powders. In recent several decades, tantalum powder producers and capacitor manufactures have conducted extensive studies on the heat treatment of tantalum powders during the development of tantalum powders having high specific surface area and small-type capacitors. The prior arts concerning the agglomeration (condensation) heat treatment of tantalum powders can be found in following patent documents: JP

2-34701, US5954856, WO99/61184, CN1197707A, CN1238251A, CN1899730A.

Deoxidation heat treatment of tantalum powders generally comprises mixing an appropriate amount of reducing agent including alkaline metals or rare earth metals or hydrides thereof with tantalum powders, subjecting to heat treatment at 700° C.-1100° C. in vacuum or inert atmosphere to condense tantalum powders and remove oxygen. The prior arts concerning the deoxidation heat treatment of tantalum powders can be found in following patent documents: U.S. Pat. No. 4,483,819, U.S. Pat. No. 4,537,641, CN1052070A, etc.

Since tantalum metal is a metal having strong affinity to oxygen, tantalum and oxygen are chemically combined to form Ta₂O₅, which is an exothermal reaction. If the surface of tantalum powders has a layer of dense oxide film, tantalum can be protected from being further oxidized. When such tantalum particles covered by the dense oxide film are heated to a temperature above 300° C., tantalum oxide film is cracked and destroyed, some oxygen dissolves in tantalum substrate, and some oxygen is dissipated or concentrated. Therefore, heated tantalum powders are oxidized starting from the surface after being cooled and contacted with oxygen-containing medium. The powders absorb new oxygen and the oxygen content increases. If the rate of absorbing oxygen cannot be effectively controlled, tantalum powders will self-ignites. Hence, oxidization-controlled passivation technique of tantalum powders has been developed. Said tantalum passivation means that when the oxidization film of tantalum powders is destroyed and in contact with oxygen-containing medium, the supplying rate of oxygen is artificially controlled to control the oxidization rate and temperature of tantalum powders under controlled condition to thereby form passivated oxide film on the surface of tantalum powders and avoid violent oxidization. Thus, tantalum powders having high specific surface area (specific surface area of above 0.1 m²/g) should subject to passivation after heat treatment.

The tantalum metal surface passivation described in present specification includes surface passivation of tantalum powders and surface passivation of porous body formed by compacting tantalum powders.

As electronic components are developed towards miniaturization, tantalum microparticles having larger specific surface area are required. As for tantalum powders having high specific surface area, when the tantalum powder per unit volume generated more heat energy during passivation, the temperature of tantalum powder during passivation rises more rapidly. During the passivation of tantalum powder after heat treatment, it was often noticed that the temperature rises suddenly. This was due to the fact that the tantalum powders began to oxidize violently, and the aerating passivation must be stopped immediately. After the temperature was lowered, aerating passivation was continued slowly. After the passivation and discharge, it was found that there were white tantalum oxide plaques on the surface of the tantalum powders, and the tantalum powder having no white tantalum oxide also had high oxygen content. If the passivation is not controlled strictly, the tantalum powder may inflame, causing significant loss. Hence, the passivation of tantalum powder becomes difficult and key technique for developing tantalum powders with high specific surface area.

Although the surface area of the porous compacts formed of tantalum powders having high specific surface area, e.g. tantalum compacts for manufacturing anodes of electrolytic capacitors, is reduced after sintering, the surface of the porous agglomerate is also oxidized and produces high temperature to make the porous agglomerate contain excessive oxygen and the tantalum wires brittle, or even cause violent oxidization of the porous tantalum agglomerate. The tantalum anode manufactured with such porous tantalum agglomerate has high leakage current. Thus, the porous agglomerate formed of tantalum powders with high specific surface area should subject to passivation treatment after sintering.

The prior arts including U.S. Pat. No. 6,927,967B2, U.S. Pat. No. 6,432,161B1, U.S. Pat. No. 6,238,456B1, CN1919508A, CN101404213A, U.S. Pat. No. 6,992,881B2, U.S. Pat. No. 7,485,256B2 and CN1899728A disclose the passivation of tantalum powders. However, these prior arts involves introducing an oxygen-containing gas at room temperature into a vacuum furnace subjected to heat treatment and cooled to room temperature or higher temperature to passivate tantalum powders. Such treatment and passivation consume long period and cause violent oxidization of tantalum powders. Chinese patent application CN101348891A discloses a method of reducing oxygen by tantalum powder controlled passivation and magnesium treatment, wherein the passivation treatment is carried out using pure oxygen. This method is not suitable for the passivation of tantalum powders with high specific surface area, and the passivation treatment consumes a long period and has a low yield.

Due to above problems in the prior art, a method and an apparatus for producing tantalum powders with low oxygen content and porous tantalum agglomerates are desired, and this method and apparatus can avoid violent oxidization during the passivation of tantalum metal surface.

SUMMARY OF THE INVENTION

In view of the problems existing in the prior art, an object of present invention is to provide a method for passivating tantalum metal surface, which can avoid the violent oxidization during the passivation. Another object is to provide an apparatus for carrying out the method for passivating tantalum metal surface.

Present invention achieves above objects by providing a method and apparatus for passivating tantalum metal surface. In this method, the tantalum metal powders are subjected to heat treatment and then cooled, and the passivation is carrier out using oxygen-containing gases at lower temperature.

In particular, present invention provides following technical solutions:

-   -   (1) A method for passivating tantalum metal surface,         characterized in that it comprises following steps:     -   a). providing tantalum metal which has been subjected to heat         treatment;     -   b). lowering the temperature of the tantalum metal to 32° C. or         below, preferably to below 30° C., and more preferably to 10°         C.-30° C., by using cooled inert gases;     -   c). introducing an oxygen-containing gas to passivate tantalum         metal surface;     -   d). optionally repeating the step c) once or more,     -   (2) A method for passivating tantalum metal surface,         characterized in that it comprises following steps:     -   a). providing tantalum metal which has been subjected to heat         treatment;     -   b). lowering the temperature of the tantalum metal to room         temperature;     -   c). introducing an oxygen-containing gas at 0° C. or below,         preferably 0° C. to −40° C., to passivate tantalum metal         surface; and     -   d). optionally repeating the step c) once or more.     -   (3) A method for passivating tantalum metal surface,         characterized in that it comprises following steps:     -   a). providing tantalum metal which has been subjected to heat         treatment;     -   b). lowering the temperature of the tantalum metal to 32° C. or         below, preferably below 30° C., and more preferably 10° C.-30°         C., by using cooled inert gases;     -   c). introducing an oxygen-containing gas at 0° C. or below, and         preferably 0° C. to −40° C., to passivate tantalum metal         surface; and     -   d). optionally repeating the step c) once or more.     -   (4) A method of passivating tantalum metal surface according to         the technical solution (1) or (2) or (3), characterized in that         said oxygen-containing gas is air, a mixture gas of inert gas         and oxygen, or a mixture gas of inert gas and air.     -   (5) A method of passivating tantalum metal surface according to         the technical solution (1) or (2) or (3), characterized in that         said oxygen-containing gas is a mixture gas of argon and air.     -   (6) A method of passivating tantalum metal surface according to         the technical solution (1) or (2) or (3), characterized in that         the concentration of oxygen in the oxygen-containing gas is 21         vol. % or below, preferably 5-20 vol. %.     -   (7) A method of passivating tantalum metal surface according to         the technical solution (1) or (3), characterized in that said         inert gas is argon.     -   (8) An apparatus for passivating tantalum metal surface         comprising a heat treatment furnace and an argon forced-cooling         device, wherein the heat treatment furnace includes: a hearth, a         shell with a water-cooling jacket constituting said hearth, an         inlet for oxygen-containing passivation gas entering the hearth,         an inlet for argon entering into the hearth, an argon outlet         positioned at upper part of the heat treatment furnace, a heater         arranged within the hearth, and a heat treatment crucible for         accommodating tantalum metal to be treated; the argon         forced-cooling device comprises a refrigerator, a heat exchange         chamber, an inlet for argon to be cooled, an outlet of cooled         argon and a circulating pump;     -   wherein the inlet for argon to be cooled is connected to the         outlet of argon at the upper part of the hearth of heat         treatment furnace; during passivation treatment, the argon with         high temperature in the heat treatment furnace comes out from         the outlet of argon, passes through connection pipelines cooled         with cooling water at periphery, and enters into the heat         exchange chamber from one side of the heat exchange chamber; in         the heat exchange chamber, the argon entered is cooled, and then         comes out from the outlet of argon at the other side of the heat         exchange chamber and enters into a circulating pump, the cooled         argon is pressed out by the circulating pump, and introduced         passing through the connection pipelines into the heat treatment         furnace from the inlet for argon at the lower part of the heat         treatment furnace to reduce the tantalum metal to be passivated         to a temperature of 32° C. or below to be passivated by the         oxygen-containing gas.     -   (9) An apparatus for passivating tantalum metal surface         comprising a heat treatment furnace and a refrigeration system         for oxygen-containing gases, wherein the heat treatment furnace         includes: a hearth, a shell with a water-cooling jacket         constituting said hearth, an inlet for the oxygen-containing gas         for passivation to enter the hearth, evacuation pipes, a heater         arranged within the hearth, and a heat treatment crucible for         accommodating tantalum metal to be treated; the refrigeration         system of oxygen-containing gases comprises: a refrigerator, a         heat exchange chamber, an inlet for oxygen-containing gases         connected with one side of the heat exchange chamber, an inlet         for argon, and an outlet for oxygen-containing gases connected         with the other side of the heat exchange chamber;     -   wherein, during the passivation treatment, the oxygen-containing         gases and argon enter from their corresponding inlets into the         heat exchanger chamber and are mixed, the mixed gases is cooled         to a temperature below 0° C. by heat exchanging with the medium         pipe in the heat exchange chamber, the cooled oxygen-containing         gases comes out from another outlet for oxygen-containing gases         of the heat exchange chamber, passes through thermal insulation         pipelines and enters into the heat treatment furnace from the         upper part of the heat treatment furnace for the passivation of         tantalum metal to be passivated.     -   (10) An apparatus for passivating tantalum metal surface         comprising a heat treatment furnace, an argon forced-cooling         device, and a refrigeration system for oxygen-containing gas,         wherein the heat treatment furnace includes: a hearth, a shell         with a water-cooling jacket constituting said hearth, an inlet         for the oxygen-containing gas for passivation to enter the         hearth, an inlet for argon entering into the hearth, an outlet         of argon positioned at upper part of the heat treatment furnace,         a heater arranged within the hearth, and a heat treatment         crucible for accommodating tantalum metal to be treated;     -   the argon forced-cooling device comprises a refrigerator, a heat         exchange chamber, an inlet for argon to be cooled, an outlet for         cooled argon and a circulating pump; wherein the inlet for argon         to be cooled is connected with the outlet of argon at the upper         part of the hearth of heat treatment furnace, during passivation         treatment, the argon with high temperature in the heat treatment         furnace comes out from the outlet of argon, passes through         connection pipelines cooled with cooling water at periphery, and         enters into the heat exchange chamber from one side of the heat         exchange chamber; in the heat exchange chamber, the argon         entered is cooled, and then comes out from the outlet for argon         at the other side of the heat exchange chamber and enters into a         circulating pump, the cooled argon is pressed out by the         circulating pump, and introduced passing through the connection         pipelines into the heat treatment furnace from the inlet for         argon at the lower part of the heat treatment furnace to thereby         reduce the tantalum metal to be passivated to a temperature of         32° C. or below; and     -   the refrigeration system of oxygen-containing gases comprises a         refrigerator, a heat exchange chamber, an inlet for         oxygen-containing gas connected with one end of the heat         exchange chamber, an inlet for argon, and an outlet for         oxygen-containing gas connected with another end of the heat         exchange chamber; during passivation treatment, the         oxygen-containing gases and argon enter from their corresponding         inlets into the heat exchanger chamber and are mixed, the mixed         gases is cooled to a temperature below 0° C. by heat exchanging         with the medium pipe in the heat exchange chamber, the cooled         oxygen-containing gases comes out from the outlet at the other         side of the heat exchange chamber, passes through thermal         insulation pipelines and enters into the heat treatment furnace         from the upper part of the heat treatment furnace for the         passivation of tantalum metal to be passivated.     -   (11) An apparatus for passivating tantalum metal surface         according to the technical solution (8) or (10), characterized         in that the tantalum metal is cooled to 10° C. to 30° C. by         means of the argon forced-cooling device so as to be passivated         by the oxygen-containing gases.     -   (12) An apparatus for passivating tantalum metal surface         according to the technical solution (9) or (10), characterized         in that the mixed gases are cooled to provide an         oxygen-containing gas for passivation of −40° C. to 0° C.

The advantages of the method for passivating tantalum metal surface are safe, reliable and high yield, and the obtained tantalum powders have low oxygen and hydrogen content, and the anodes and tantalum electrolytic capacitors manufactured from the tantalum powders exhibit good electric properties.

It should be understood that above general descriptions and following detailed description in connection with drawings and the detailed description of preferred examples are demonstrative descriptions which are used for further explaining the claimed invention, not for limiting the invention.

DESCRIPTION OF DRAWINGS

FIG. 1 is schematic diagram of an apparatus for passivating tantalum metal surface in the prior art.

FIG. 2 shows an example of an apparatus for passivating tantalum metal surface with an inert gas forced-cooling device according to present invention.

FIG. 3 shows an example of an apparatus for passivating tantalum metal surface with a refrigeration system of oxygen-containing gas according to present invention.

FIG. 4 shows an example of an apparatus for passivating tantalum metal surface with an inert gas forced-cooling device and a refrigeration system of oxygen-containing gas according to present invention.

FIG. 5 shows another schematic diagram of an apparatus for passivating tantalum metal surface in the prior art.

FIG. 6 shows another example of an apparatus for passivating tantalum metal surface with an inert gas forced-cooling device according to present invention.

FIG. 7 shows another example of an apparatus for passivating tantalum metal surface with a refrigeration system of oxygen-containing gas according to present invention.

FIG. 8 shows another example of an apparatus for passivating tantalum metal surface with an inert gas forced-cooling device and a refrigeration system of oxygen-containing gas according to present invention.

EMBODIMENTS

Present invention is further described hereinafter with reference to the drawings and preferred examples:

In the specification, the unit ppm indicates “parts per million” based on mass ratio, unless otherwise expressly stated.

Present invention provides a method for passivating tantalum metal surface. In the method of present invention, the tantalum metal to be heat treated and passivated can be chemically reduced tantalum powders which have not been heat treated, e.g. tantalum powders prepared by reducing potassium tantalum fluoride with sodium, an raw material powder obtained by hydrogenation and grinding of tantalum ingots, and heat treated tantalum powders, and porous tantalum agglomerates formed by compacting tantalum powders, and so on. Before heat treatment, the tantalum powders are preferably pelletized, particularly subjected to spheroidizing granulation. During the granulation of tantalum powders, any chemical substance benefiting to control the shrinkage rate of tantalum powders at high temperature sintering and reducing surface area loss at required ratio can be added as fire resistance agent, such as a substance containing phosphor, nitrogen, boron, oxygen. In the method of present invention, the tantalum powders can subject to heat treatment by known techniques, for example, the methods disclosed in CN1410209A, CN1238251A and CN1899730A, which are incorporated herein by reference.

In the method of present invention, an inert gas forced-cooling device can be used to cool heat treated tantalum metal to a temperature below 32° C. Said inert gas can be argon, helium, xenon or a mixture thereof. However, in view of cost, argon is preferably used to carry out forced-cooling.

According to the method of present invention, the particle shape of tantalum powders to be heat treated is not limited; it can be particulate, sheet, multiangular shape or any combination thereof. The specific surface area of the tantalum powders is not specifically required and can be 0.1 m²/g-10 m²/g, preferably 0.2 m²/g-5 m²/g.

The deoxidization heat treatment of tantalum powders in reductive atmosphere can be carried out by known techniques in the art. Generally, a small amount of a reducing agent having an affinity to oxygen greater than that of tantalum to oxygen can be added in the tantalum powders, such as alkaline earth metals, rare earth metals, and hydrides thereof; most commonly, a metal magnesium powder of 0.5%-4% based on the weight of tantalum is added to the tantalum powder.

FIG. 1 is a diagram of an apparatus 100 for passivating heat treated tantalum metal surface in the prior art. The apparatus for passivating heat treated tantalum metal surface comprises: a hearth 110, a shell 111 with a water cooling jacket having a water inlet 111-1 and a water outlet 111-2, the shell constitutes the hearth 110, and a vacuum pressure meter 112 communicated with the hearth 110, an inlet 120 of the oxygen-containing passivation gas entering into the hearth 110, an inlet 140 of argon, evacuating pipelines 141, a heat insulation screen 130 arranged in the hearth, a heater 150 arranged in the heat insulation screen 130, a thermocouple 160 for measuring temperature, a heat treatment crucible 180, and a tantalum powder 170 to be treated contained in the crucible 180.

FIG. 2 is a diagram of an apparatus for passivating tantalum metal surface with an argon forced-cooling device according to present invention. The apparatus for passivating tantalum metal surface comprises: a hearth 210, a shell 211 with a water cooling jacket having a water inlet 211-1 and a water outlet 211-2, the shell constitutes the hearth 210, and a vacuum pressure meter 212 communicated with the hearth 210, an inlet 220 of oxygen-containing gas for passivation, an inlet 240 of argon, evacuating pipelines 241, a heat insulation screen 230 arranged in the hearth 210, a heater 250 arranged in the heat insulation screen 230, a thermocouple 260 for measuring temperature, a heat treatment crucible 280, and a tantalum powder 270 to be treated charged in the crucible 280. The apparatus for passivating tantalum metal surface further comprises a device 200A for forced-cooling argon; the components in the device 200A for forced-cooling argon and the functions thereof are as follows: an outlet 207 at the upper part of the heat treatment furnace, the argon with high temperature in the furnace comes out from the outlet 207 of argon, passes through connection pipelines 208 cooled with cooling water at periphery, and enters into the heat exchange chamber 201 from the inlet 202 of argon at one side of the heat exchange chamber. In the heat exchange chamber 201 there is a medium pipeline 204 cooled by a refrigerator 200, the refrigerator 200 allows a cooling medium to pass through the heat exchanger chamber 201; in the heat exchange chamber 201, the argon entered is cooled, and then comes out from the outlet 205 of argon at the other side of the heat exchange chamber, passes through a pipeline 206 and enters into a circulating pump 209, the cooled argon is pressed out by the circulating pump 209, and introduced passing through the connection pipelines into the heat treatment furnace from the inlet 240 of argon at the lower part of the heat treatment furnace. (wherein the cooling water at the periphery of pipeline 208 enters from 208-1 at one side of the heat exchange chamber adjacent to the refrigerator heat exchange chamber, and comes out from 208-2 adjacent to one side of the heat treatment furnace, before the tantalum powder is passivated, it is forcedly cooled by means of the argon forced-cooling device to reduce the temperature of the tantalum powder to 30° C. or below, preferably to 10° C.-30° C. to effectively control the oxidization of tantalum powder and avoid the violent oxidization of tantalum powder. During the forced-cooling with argon, the pressure of the system is maintained between 0.09 MPa-0.11 MPa by supplying argon to the circulating system or exhausting.

FIG. 3 shows an apparatus for passivating tantalum metal surface with an oxygen-containing gas refrigerating system for passivating tantalum metal surface. The apparatus for passivating tantalum metal surface comprises: a hearth 310, a shell 311 with a water cooling jacket having a water inlet 311-1 and a water outlet 311-2, the shell constitutes the hearth 310, and a vacuum pressure meter 312 communicated with the hearth 310, an inlet 320 of oxygen-containing gas for passivation at the upper part of the hearth, an inlet 340 of argon, evacuating pipelines 341, a heat insulation screen 330 arranged in the hearth, a heater 350 arranged in the heat insulation screen 330, a thermocouple 360 for measuring temperature, a heat treatment crucible 380, and a tantalum powder 370 to be treated contained in the crucible 380. The apparatus for passivating tantalum metal surface further comprises a refrigerating system 390A of oxygen-containing gas for passivation, the refrigerating system 390A of oxygen-containing gas for passivation comprising: a refrigerator 390, a heat exchange chamber 391, the medium cooled by the refrigerator passes through the heat exchange chamber 391; the oxygen-containing gas and argon enter from the inlet 392 and the inlet 393 of argon respectively into the heat exchanger chamber 391 and are mixed, the mixed oxygen-containing gas and the refrigeration medium pipe 394 connected with the refrigerator 390 undergo heat exchange, the cooled oxygen-containing gas comes out from the outlet 395 at the other side of the heat exchange chamber 391, passes through thermal insulation pipelines 396 connecting the outlet 395 and the inlet 320 at the upper part of the heat treatment furnace and enters into the hearth 310; in which there is a pressure meter 398 communicated with the heat exchange chamber 391, a thermometer 397 is arranged near the outlet 395 of oxygen-containing gases; and a water outlet 399 arranged at the bottom of the heat exchanger 391. When the passivation of a batch of tantalum metal is completed, each component in the heat exchanger is dried using hot air, the melted water flows out from the water outlet 399. The oxygen-containing gases is cooled to below 0° C., preferably below −10° C., more preferably −10° C. to −40° C.

FIG. 4 is a schematic diagram of an apparatus for passivating tantalum metal surface with an argon forced-cooling device and a refrigeration system of oxygen-containing gas according to present invention, comprising: a hearth 410, a shell 411 with a water cooling jacket having a water inlet 411-1 and a water outlet 411-2, the shell constitutes the hearth 410, and a vacuum pressure meter 412 communicated with the hearth 410, an inlet 420 of oxygen-containing gas for passivation, an inlet 440 of argon, evacuating pipelines 441, a heat insulation screen 430 arranged in the hearth, a heater 450 arranged in the heat insulation screen 430, a thermocouple 460 for measuring temperature, a heat treatment crucible 480, and a tantalum powder 470 to be treated contained in the crucible 480, characterized in that the apparatus for passivating tantalum metal surface further comprises: an argon forced-cooling device 400A and a refrigerating system 490A of oxygen-containing gas, wherein the components in the device 400A for forced-cooling argon and the functions thereof are as follows: an argon outlet 407 at the upper part of the heat treatment furnace, the argon with high temperature in the furnace comes out from the outlet 407 of argon, passes through connection pipelines 408 cooled with cooling water entering from 408-1 and coming out from 408-2 at periphery, and enters into the heat exchange chamber 401 from one side of the heat exchange chamber 401, in the heat exchange chamber 401 there is a medium pipeline 404 cooled by a refrigerator, in the heat exchange chamber 401, the argon entered is cooled, and comes out from the outlet 405 of argon at the other side of the heat exchange chamber 401, passes through a pipeline 406 and enters into a circulating pump 409, the cooled argon is pressed out by the circulating pump 409, and introduced passing through the connection pipelines into the heat treatment furnace 410 from the inlet 440 at the lower part of the heat treatment furnace, the components in the refrigeration system 490A of oxygen-containing gas and their functions are as follows: the cooling medium is cooled by the refrigerator 490; the cooled medium flows passing through the medium pipeline 494 into the heat exchange chamber 491, in which there is a pressure meter 498 communicated with the heat exchange chamber 491; in the heat exchange chamber 491, the oxygen-containing gas and argon enter from their corresponding inlets 492 and 493 respectively into the heat exchange chamber 491 and are mixed; the mixed oxygen-containing gas is cooled by heat exchanging with the medium pipeline 494 in the heat exchange chamber 491, the cooled oxygen-containing gas comes out from another outlet 495 of the heat exchange chamber 491, passes through thermal insulation pipelines 496 and enters into the heat treatment furnace 410 from the inlet 420 at the upper part of the heat treatment furnace, a thermometer 497 is arranged near the outlet of the oxygen-containing gas, the thermometer being used for measuring the temperature of oxygen-containing gas; a water outlet 499 is arranged at the bottom of the heat exchange chamber 491. When the passivation of a batch of tantalum metal is completed, each component in the heat exchanger is dried using hot air, the melted water flows out from the water outlet 499.

FIG. 5 is a schematic diagram of a prior apparatus for passivating tantalum metal surface after the tantalum powder is subjected to deoxidization heat treatment by external heating (not shown), comprising: a deoxidization heat treatment reaction vessel 510, an upper cover 511, an argon inlet pipe 540 arranged on the upper cover 511, an evacuating pipeline 541, a nitrogen inlet pipe 542, an inlet pipe 520 of oxygen-containing gas for passivation, a vacuum pressure meter 512 for measuring the pressure in the reaction vessel, a tantalum crucible 580 arranged in the reaction vessel 510, a tantalum powder mixed with magnesium powder contained in the crucible 580, a thermocouple 561, 562 and 563 for measuring the temperature of upper part, middle part and lower part of the reaction vessel, respectively, and a thermal insulation screen assembly 530 located in the upper part of the crucible 580.

FIG. 6 is a schematic diagram of an apparatus for passivating tantalum metal surface after the tantalum powder is subjected to deoxidization heat treatment by external heating (not shown) with an inert gas forced-cooling device according to present invention, comprising: a deoxidization heat treatment reaction vessel 610, an upper cover 611, an argon inlet pipe 640 arranged on the upper cover 611 and extended into the lower part of the reaction vessel 610, an evacuating pipeline 641, a nitrogen inlet pipe 642, an inlet pipe 620 of oxygen-containing gas for passivation, a vacuum pressure meter 612 for measuring the pressure in the reaction vessel, a tantalum crucible 680 arranged in the reaction vessel 610, a tantalum powder 670 mixed with magnesium powder contained in the crucible 680, thermocouples 661, 662 and 663 for measuring the temperature of upper part, middle part and lower part of the reaction vessel, respectively, and a thermal insulation screen assembly 630 located in the upper part of the crucible 680, characterized by further comprising an argon forced-cooling device 600A, the device 600A for forced-cooling argon comprising: an argon outlet 607 at the upper part of the reaction vessel 610, the argon with high temperature in the furnace comes out from the outlet 607 of argon, passes through connection pipelines 608 cooled with cooling water entering from 608-1 and coming out from 608-2 at periphery, and enters into the heat exchange chamber 601 from one side of the heat exchange chamber 601, in the heat exchange chamber 601 there is a medium pipeline 604 cooled by a refrigerator, in the heat exchange chamber 601, the argon entered is cooled and comes out from the outlet 605 of argon at the other side of the heat exchange chamber 601, passes through a pipeline 606 and enters into a circulating pump 609, the cooled argon is pressed out by the circulating pump 609, and introduced passing through the connection pipelines into the heat treatment furnace 610 from the inlet 640 at the lower part of the heat treatment furnace.

By forced-cooling with argon, the temperature of tantalum powder is reduced to 30° C. or below, preferably to 10° C. to 20° C., before the passivation of tantalum powder.

FIG. 7 is a schematic diagram of an apparatus for passivating tantalum metal surface after the tantalum powder is subjected to deoxidization heat treatment by external heating (not shown in the figure) with a refrigeration system of oxygen-containing gas according to present invention, comprising: a deoxidization heat treatment reaction vessel 710, an upper cover 711, an argon inlet pipe 740 arranged on the upper cover 711, an evacuating pipeline 741, a nitrogen inlet pipe 742, an inlet pipe 720 of oxygen-containing gas for passivation, a vacuum pressure meter 712 for measuring the pressure in the reaction vessel, a tantalum crucible 780 arranged in the reaction vessel 710, a tantalum powder 770 mixed with magnesium powder contained in the crucible 780, thermocouples 761, 762 and 763 for measuring the temperature of upper part, middle part and lower part of the reaction vessel, respectively, and a thermal insulation screen assembly 730 located in the upper part of the crucible 780, characterized by further comprising a refrigeration system 790A of oxygen-containing gas for passivation, the refrigeration system 790A of oxygen-containing gas comprising: a refrigerator 490 for refrigerating cooling medium; the cooled medium flows passing through the medium pipeline 794 into the heat exchange chamber 791, in which there is a pressure meter 798 communicated with the heat exchange chamber 791; in the heat exchange chamber 791, the oxygen-containing gas and argon enter from their corresponding inlets 792 and 793 into the heat exchange chamber 791 and are mixed; the mixed oxygen-containing gas undergo heat exchange reaction with the medium pipeline 794 in the heat exchange chamber 791, and thus is cooled, the cooled oxygen-containing gas comes out from outlet 795 at the other side of the heat exchange chamber 791, passes through thermal insulation pipelines 796 and enters into the reaction vessel 710 from the inlet 720 at the upper part of the reaction vessel, a thermometer 797 is arranged near the outlet of the oxygen-containing gas, the thermometer being used for measuring the temperature of oxygen-containing gas; a water outlet 799 is arranged at the bottom of the heat exchange chamber 791.

When the passivation of a batch of tantalum metal is completed, each component in the heat exchanger is dried using hot air, the melted water flows out from the water outlet 799.

FIG. 8 is a schematic diagram of an apparatus for passivating tantalum metal surface after the tantalum powder is subjected to deoxidization heat treatment with an inert gas forced-cooling device and a refrigeration system of oxygen-containing gas according to present invention, comprising: a deoxidization heat treatment reaction vessel 810, an upper cover 811, an argon inlet pipe 840 arranged on the upper cover 811 and extended into the lower part of the reaction vessel 810, an evacuating pipeline 841, a nitrogen inlet pipe 842, an inlet pipe 820 of oxygen-containing gas for passivation, a vacuum pressure meter 812 for measuring the pressure in the reaction vessel, a tantalum crucible 880 arranged in the reaction vessel 810, a tantalum powder 870 mixed with magnesium powder contained in the crucible 880, thermocouples 861, 862 and 863 for measuring the temperature of upper part, middle part and lower part of the reaction vessel, respectively, and a thermal insulation screen assembly 830 located in the upper part of the crucible 880, characterized by further comprising an argon forced-cooling device 800A and a refrigerating system 890A of oxygen-containing gas, the components of the device 800A for forced-cooling argon and the functions thereof are as follows: an argon outlet 807 arranged at the upper part of the reaction vessel 810, the argon with high temperature in the furnace comes out from the outlet 807 of argon, passes through connection pipelines 808 cooled with cooling water entering from 808-1 and coming out from 808-2 at periphery, and enters into the heat exchange chamber 801 from one side of the heat exchange chamber 801, in the heat exchange chamber 801 there is a medium pipeline 804 cooled by a refrigerator, in the heat exchange chamber 801, the argon entered is cooled and comes out from the outlet 805 of argon at the other side of the heat exchange chamber 801, passes through a pipeline 806 and enters into a circulating pump 809, the cooled argon is pressed out by the circulating pump 809 and introduced passing through the connection pipelines into the heat treatment furnace 810 from the inlet 840 at the lower part of the reaction vessel. The components in the refrigeration system 890A of oxygen-containing gas and functions thereof are as follows: the cooling medium is cooled by the refrigerator 890; the cooled medium flows passing through the medium pipeline 894 into the heat exchange chamber 891, in which there is a pressure meter 898 communicated with the heat exchange chamber 891; in the heat exchange chamber 891, the oxygen-containing gas and argon enter from their corresponding inlets 892 and 893 into the heat exchange chamber 891 and are mixed; the mixed oxygen-containing gas undergoes heat exchange with the medium pipeline 894 in the heat exchange chamber 891 and thereby is cooled, the cooled oxygen-containing gas comes out from outlet 895 at the other side of the heat exchange chamber 891, passes through thermal insulation pipelines 896 and enters into the reaction vessel 810 from the inlet 820 at the upper part of the reaction vessel, a thermometer 897 is arranged near the outlet of the oxygen-containing gas, the thermometer being used for measuring the temperature of oxygen-containing gas; a water outlet 899 is arranged at the bottom of the heat exchange chamber 891.

When the passivation of a batch of tantalum metal is completed, each component in the heat exchanger is dried using hot air, the melted water flows out from the water outlet 899.

In present invention, charging tantalum powder into the heat treatment furnace is not specially limited. However, in consideration of heat homogeneity, nitridation and passivation homogeneity and sufficiency, the thickness of tantalum powder is preferably 60 mm or below, and more preferably 40-50 mm; For the purpose of safety and higher yield, the tantalum powder is preferably gently charged in a tantalum crucible and leveled. Present invention usually employs circular or square crucible with shallow depth, such as, tantalum crucible having length×width×depth=about 350 mm×210 mm×75 mm.

The temperature of heat treatment and holding time of tantalum powder is determined based on different types of tantalum powders and requirements, generally holding for 30-90 minutes at a temperature of 900° C.-1400° C. and a vacuum pressure lower than 1.33×10⁻¹ Pa.

The heat treated tantalum powder is optionally nitridated by introducing nitrogen during cooling.

After subjecting to temperature holding at 900° C.-1400° C., the tantalum powder is cooled in vacuum furnace, and can be cooled by a shell with cooling water jacket, the tantalum powder is cooled in vacuum to a temperature, e.g. about 500° C. or below, cooled with room temperature argon to about 80° C. or below, and then subjected to forcedly circulation cooling with argon below room temperature so that the tantalum powder is cooled to 30° C. or below, preferably to 20° C. or below, e.g. to 10° C. to 20° C., and then subjected to passivation treatment by introducing an oxygen-containing gas.

The oxygen-containing gas is a mixed gas consisting of argon and oxygen, in consideration of economics, the oxygen-containing gas is preferably a mixed gas consisting of air and argon. According to present invention, the concentration of oxygen in the oxygen-containing gas is 21 vol. % or below; the lower the concentration of oxygen, the oxidation of tantalum can be controlled more effectively. Since the specific heat of gas lower, in consideration of effect, it is desirable that the concentration of oxygen in the oxygen-containing gas is as low as possible. However, in consideration of yield and economics, at the beginning of passivation, preferably the content of oxygen in the oxygen-containing gas is 5-15 vol. %.

As for tantalum powder having low specific surface area, it is enough that the passivation is carried out once. As for tantalum powder having high specific surface area, it is preferred that the passivation is carried out twice or more. The first passivation is carried out using a gas with low oxygen content, and then the oxygen concentration of oxygen-containing gas is increased gradually, the oxygen concentration is up to the oxygen concentration in air, about 21 vol. %.

According to present invention, an oxygen-containing gas and a dilution gas, e.g., argon, were introduced from their respective inlets into the heat exchange chamber in a volume ratio calculated by gas pressure, the gasses are mixed and underwent heat exchange with the heat exchanger, the temperature of the discharged oxygen-containing gas was measured at the outlet. The temperature of the oxygen-containing gas described in present invention means the temperature of discharged gas measured at the outlet.

When tantalum powder was passivated, the heat treatment furnace was evacuated to about 200 Pa, and then the oxygen-containing gas was continuously or discontinuously introduced into the heat treatment furnace to make the final pressure in the heat treatment furnace reach to about 0.1 MPa.

The heat treatment described herein means the heating course of tantalum powder at a temperature of above 300° C. in vacuum or an inert atmosphere or reductive atmosphere, and includes the sintering of porous tantalum compact, e.g., the sintering for manufacturing anode of tantalum electrolytic capacitor, and a device similar to heat treatment of tantalum powder can be employed, e.g. a device as shown in FIG. 2-FIG. 4.

The oxygen content of tantalum powder disclosed herein was determined by means of TC-436 oxygen nitrogen joint determinator; the hydrogen content of tantalum powder was determined by means of RH-404 hydrogen content determinator. The wet electronic property data of tantalum powder disclosed herein were measured as follows: the tantalum powder was compacted into a cylindrical compact with a density of 4.5 g/cm³, a diameter of 3.0 mm and a height of 4.72 mm, in which 0.3 mm tantalum wire was embedded, each compact containing about 150 mg of tantalum powder; the compact was sintered at 1320° C. for 10 minutes to form an agglomerate; the agglomerate was placed in 0.1 mass % phosphoric acid at 80° C., the voltage was raised to 30 V at a current density of 60 mA/g and the voltage was kept for 120 minutes to form an anode in which dielectric oxide film was covered on the surface of tantalum particles; the leakage current of the anode was determined in 0.1 mass % phosphoric acid at 25° C., and the specific electric capacity (specific capacity) and loss were determined in 20 mass % of sulfuric acid solution.

In order to further explain present invention, the preferred embodiments of present invention are described as follows by combining examples and drawings. However, it should be understood that these descriptions are only further explanation of the features and advantages of present invention, but not limitation to the scope of the invention.

EXAMPLES Example 1

A feedstock powder which was prepared by reducing potassium tantalum fluoride with sodium is provided; the feedstock powder has a specific surface area of 1.82 m²/g, a bulk density of 0.51 g/cm³, and oxygen content of 6200 ppm. The raw material powder, was mixed with 120 ppm of phosphorus based on the weight of the tantalum powder, spheroidizing granulated to obtain spherical particles with a bulk density of 1.02 g/cm³. The spheroidizing granulated tantalum powder was charged into a crucible, and the crucible was placed in a tantalum powder heat treatment passivation device as shown in FIG. 4, heated in vacuum below 1.33×10⁻¹ Pa to 1200° C. and held for 30 minutes, and then the heating was stopped and the temperature was lowered to 200° C.; argon was introduced to lower the temperature to 80° C., the forced-cooling argon system 400A was actuated, the argon with high temperature in the heat treatment furnace came out from the outlet 407, passed through the pipeline 408 cooled with cooling water, entered into the heat exchange chamber 401 from the gas inlet 402 and underwent heat exchange with the refrigerating medium pipe 404 connected with the refrigerator; argon was cooled through heat exchange, the cooled argon came out from the outlet 405, pumped by using a circulating pump 409 to pass through the pipeline 406 and enter the heat treatment furnace from the gas inlet 440 of the heat treatment furnace, constituting circulation of argon. The circulated argon caused the crucible and tantalum powder in the heat treatment furnace cooled, after the cooling was carried out for about 2 hours, the temperature in the furnace was lowered to 25° C., and the tantalum powder was passivated. The passivation process comprises evacuating the gas in the furnace from the aeration pipeline 441 to a vacuum of about 200 Pa, the refrigeration system 490A of oxygen-containing gas was actuated to make air and argon enter the heat exchange chamber 491 from 492 and 493 respectively according to following conditions, mix and undergo heat exchange with 494, and then came out from the outlet 495, passed through the thermal insulation pipeline 496, and entered the hearth 410 from the inlet 420; first, the oxygen-containing gas with an oxygen concentration of about 5 vol. % (1 volume of air and 3 volume of argon were introduced by pressure meter from the inlet 492 and the outlet 493 into the heat exchange chamber 491) underwent heat exchange with the refrigerating medium pipe 494 connected with the refrigerator and thereby was cooled, the oxygen-containing gas at a temperature of −10° C. to −20° C. came out from the outlet 495 of oxygen-containing gas, passed through the thermal insulation pipe 496 and entered the heat treatment furnace from the gas inlet 420 at the upper part of the heat treatment furnace, the pressure was increased in 8 stages and 3 hours from 200 Pa to OA MPa: (200 Pa-0.005 MPa)/30 minutes, (0.005 MPa-0.01 MPa)/30 minutes, (0.01 MPa-0.02 MPa)/20 minutes, (0.02 MPa-0.03 MPa)/20 minutes, (0.03 MPa-0.045 MPa)/20 minutes, (0.045M Pa-0.06 MPa)/20 minutes, (0.06 MPa-0.08 MPa)/20 minutes, (0.08 MPa-0.1 MPa)/20 minutes, total 3 hours; second, the oxygen-containing gas at −10° C. to −20° C. with an oxygen concentration of about 10 vol. % (1 volume of air and 1 volume of argon were mixed) were increased from 200 Pa to 0.1 MPa in 3 hours according to the first aeration procedure; third, the pressure was increased from 200 Pa to 0.1 MPa in 3 hours using air at −10° C. to −20° C. according to the same procedure as the first procedure; fourth, the pressure was increased from 200 Pa to 0.1 MPa in 4 stages total 2 hours using air at −10° C. to −20° C.: (200 Pa-0.01 MPa)/30 minutes, (0.01 MPa-0.03 MPa)/30 minutes, (0.03 MPa-0.06 MPa)/30 minutes, (0.06 MPa-0.10 MPa)/30 minutes. The four passivations were carried out in total 11 hours. During the whole procedure, the temperature in the furnace was firstly elevated gradually to 28° C., then the temperature was gradually steady and varied between 25° C. and 28° C., and finally the temperature was lowered gradually to 25° C. After discharging, the tantalum powder was taken out, and no violent oxidation phenomenon occurred. The heat treated tantalum powder was passed through 80 mesh screening to obtain S-1h tantalum powder. The oxygen and hydrogen contents of the tantalum powder were analyzed, the results were shown in Table 1. 2 wt % Magnesium powder based on the tantalum powder was blended to form a mixed powder, the mixed powder was charged into the tantalum powder deoxidization reaction vessel as shown in FIG. 6, held at 850° C. for 3 hours to carry out deoxidization treatment, the heating was stopped, and the temperature was lowered, and the treated tantalum powder was nitridated at 280° C., and then forcedly cooled with argon, when the temperature of tantalum powder was lowered to 15° C., according to the passivation procedure similar to the heat treatment as described above, an oxygen-containing gas at 31° C. was introduced, and passivation was carried out in 4 times using an oxygen-containing gas with an oxygen concentration of about 5 vol. %, 10 vol. %, 21 vol. % and 21 vol. %, the first 3 passivations were carried out for 3 hours each, and the last passivation was carried out for 2 hours, total 11 hours. After discharging, the passivated tantalum powder was pickled, washed with water, and dried to obtain S-1d tantalum powder. The oxygen and hydrogen contents of the tantalum powder were analyzed, the results were shown in Table 1. The electric performance of the tantalum powder was determined, and the results were shown in Table 2.

Example 2

The feedstock tantalum powder, as employed in Example 1, was charged in the tantalum powder heat treatment furnace with an argon forced-cooling device as shown in FIG. 2, and subjected to heat treatment according to the same conditions in Example 1, when the temperature of tantalum powder was lowered to about 200° C., argon was introduced, and the forced-cooling argon system 200A was actuated, the argon with high temperature in the heat treatment furnace came out from the outlet 207 at the upper part of the furnace, passed through water cooled pipeline 208, entered into the heat exchange chamber 201 from the gas inlet 202 and underwent heat exchange with the refrigerating medium pipe 204 connected with the refrigerator 200; argon was cooled through heat exchange, the cooled argon came out from the outlet 205, passed through pipeline 206, pumped by using a circulating pump 209 to enter the heat treatment furnace 210 from the gas inlet 240 of the heat treatment furnace, constituting circulation of argon; the circulated argon caused the crucible and tantalum powder in the heat treatment furnace cooled, after the cooling was carried out for about 4 hours, the crucible and tantalum powder were forcedly cooled argon to a temperature of 10° C., and the tantalum powder was passivated. The heat treatment furnace was evacuated to about 200 Pa; first, the oxygen-containing gas at 32° C. with an oxygen concentration of about 5 vol. % was increased in 8 stages and 4 hours from 200 Pa to 0.1 MPa: (200 Pa-0.005 MPa)/30 minutes, (0.005 MPa-0.01 MPa)/30 minutes, (0.01 MPa-0.02 MPa)/30 minutes, (0.02 MPa-0.03 MPa)/30 minutes, (0.03 MPa-0.045 MPa)/30 minutes, (0.045 MPa-0.06 MPa)/30 minutes, (0.06 MPa-0.08 MPa)/30 minutes, (0.08 MPa-0.1 MPa)/30 minutes; second, the oxygen-containing gas at 32° C. with an oxygen concentration of about 10 vol. % was increased from 200 Pa to 0.1 MPa in 4 hours according to the first aeration procedure; third, the pressure was increased from 200 Pa to 0.1 MPa in 4 hours using air at 32° C. according to the same procedure as the first procedure; fourth, the oxygen-containing gas was increased from 200 Pa to 0.1 MPa in 4 stages total 2 hours using air at 32° C.: (200 Pa-0.01 MPa)/30 minutes, (0.01 MPa-0.03 MPa)/30 minutes, (0.03 MPa-0.06 MPa)/30 minutes, (0.06 MPa-0.10 MPa)/30 minutes. The four passivations were carried out in total 14 hours. During the whole procedure, the temperature in the furnace was firstly elevated gradually to 33° C., then the temperature was gradually steady and varied between 28° C. and 32° C. After discharging, the tantalum powder was taken out, no violent oxidation phenomenon occurred. The heat treated tantalum powder was passed through 80 mesh screening to obtain S-2h tantalum powder. The oxygen and hydrogen contents of the tantalum powder were analyzed, the results were shown in Table 1, 2 wt % Magnesium powder based on the tantalum powder was blended in the S-2h tantalum powder to form a mixed powder, the mixed powder was charged into the tantalum powder deoxidization reaction vessel as shown in FIG. 7, held at 850° C. for 3 hours to carry out deoxidization treatment, the heating was stopped, and the temperature was lowered, and the treated tantalum powder was nitridated at 280° C., and then the temperature of the tantalum powder in the reaction vessel was lowered to 31° C., an oxygen-containing gas at −10° C. to −40° C. was introduced in 4 times, according to the passivation procedure similar to the heat treatment as described above, and the tantalum powder was passivated using an oxygen-containing gas with an oxygen concentration of about 5 vol. %, 10 vol. %, 21 vol. % and 21 vol. %, the first 3 passivations were carried out for 3 hours each, and the last passivation was carried out for 2 hours, total 11 hours. After discharging, the passivated tantalum powder was pickled, washed with water, and dried to obtain S-2d tantalum powder. The oxygen and hydrogen contents of the tantalum powder were analyzed, the results were shown in Table 1. The electric performance of the tantalum powder was determined, and the results were shown in Table 2.

Example 3

The heat treatment device shown in FIG. 3 was used, and the same tantalum powder as in Example 1 was subjected to heat treatment under the same condition as described in Example 1. After the heat treatment, the shell was cooled with water to lower the temperature, and argon was introduced for 12 hours to lower the temperature to 30° C., and the tantalum powder was passivated. The passivation process comprises: evacuating the argon in the furnace to about 200 Pa, the refrigeration system 390A of oxygen-containing gas was actuated to make air and argon enter into the heat exchange chamber 391 respectively from 392 and 393 according to following conditions, mix and undergo heat exchange with 394, and then came out from the outlet 395, passed through the thermal insulation pipeline 396, and entered the hearth 310 from the inlet 320; first, the oxygen-containing gas with an oxygen concentration of about 5 vol. % was cooled to −20° C. to −40° C. and increased in stages from 200 Pa to 0.1 MPa: (200 Pa-0.005 MPa)/30 minutes, (0.005 MPa-0.01 MPa)/30 minutes, (0.01 MPa-0.02 MPa)/30 minutes, (0.02 MPa-0.03 MPa)/30 minutes, (0.03 MPa-0.045 MPa)/30 minutes, (0.045 MPa-0.06 MPa)/30 minutes, (0.06 MPa-0.08 MPa)/30 minutes, (0.08 MPa-0.1 MPa)/30 minutes, total 4 hours; second, the oxygen-containing gas at −20° C. to −40° C. with an oxygen concentration of about 10 vol. % was increased from 200 Pa to 0.1 MPa in 4 hours according to the first aeration procedure; third, the pressure was increased from 200 Pa to 0.1 MPa in 4 hours using air at −20° C. to −40° C. according to the same procedure as the first procedure; fourth, the pressure was increased from 200 Pa to 0.1 MPa in 4 stages using air at −20° C. to −40° C.: (200 Pa-0.01 MPa)/30 minutes, (0.01 MPa-0.03 MPa)/30 minutes, (0.03 MPa-0.06 MPa)/30 minutes, (0.06 MPa-0.10 MPa)/30 minutes. The four passivations were carried out in total 14 hours. The temperature in the furnace was firstly elevated gradually to 35° C., then the temperature was gradually steady and varied between 32° C. and 35° C. After discharging, the tantalum powder was taken out, no violent oxidation phenomenon occurred. The heat treated tantalum powder was passed through 80 mesh screening to obtain S-3h tantalum powder. The oxygen and hydrogen contents of the tantalum powder were analyzed, the results were shown in Table 1. 2 wt % magnesium powder based on the tantalum powder was blended in the tantalum powder S-3h to form a mixed powder, the mixed powder was charged into the tantalum powder deoxidization reaction vessel as shown in FIG. 8, held at 850° C. for 3 hours to carry out deoxidization treatment, the heating was stopped, and the temperature was lowered, and the treated tantalum powder was nitridated at 280° C., and then forcedly cooled with argon, when the temperature of tantalum powder was lowered to 15° C., an oxygen-containing gas at −10° C. to −40° C. was introduced in 4 times, according to the passivation procedure similar to the heat treatment as described above, the tantalum powder was passivated with an oxygen-containing gas with an oxygen concentration of about 5 vol. %, 10 vol. %, 21 vol. % and 21 vol. %, the first 3 passivations were carried out for 3 hours each, and the last passivation was carried out for 2 hours, total 11 hours. After discharging, the passivated tantalum powder was pickled, washed with water, and dried to obtain S-3d tantalum powder. The oxygen and hydrogen contents of the tantalum powder were analyzed, the results were shown in Table 1. The electric performance of the tantalum powder was determined, and the results were shown in Table 2.

Comparative Example 1

The same tantalum powder as in Example 1 was employed, and the heat treatment was carried out at same temperature, after heating was stopped, the temperature was lowered to 200° C. in vacuum, and argon was introduced to cool for 12 hours, when the temperature was lowered to 32° C., the passivation was begun; the passivation process comprises: evacuating the argon in the furnace to about 200 Pa, first, air at 31° C. was introduced into the heat treatment furnace in 8 stages to increase the pressure in the furnace from 200 Pa to 0.1 MPa: (200 Pa-0.005 MPa)/120 minutes, (0.005 MPa-0.01 MPa)/60 minutes, (0.01 MPa-0.02 MPa)/60 minutes, (0.02 MPa-0.03 MPa)/60 minutes, (0.03 MPa-0.045 MPa)30 minutes, (0.045 MPa-0.06 MPa)/30 minutes, (0.06 MPa-0.08 MPa)/30 minutes, (0.08 MPa-0.1 MPa)/30 minutes, total 7 hours, wherein the temperature elevated suddenly for 6 times during the aeration, the highest temperature was up to 60° C.; when it was found that the temperature elevated suddenly, the aeration was stopped immediately; and after the temperature was lowered to about 32° C., the aeration in the furnace was carried out again. Second, air at 31° C. was introduced into the heat treatment furnace in 8 stages to increase the pressure in the furnace from 200 Pa to 0.1 MPa: (200 Pa-0.005 MPa)/60 minutes, (0.005 MPa-0.01 MPa)/60 minutes, (0.01 MPa-0.02 MPa)/60 minutes, (0.02 MPa-0.03 MPa)/60 minutes, (0.03 MPa-0.045 MPa)30 minutes, (0.045 MPa-0.06 MPa)/30 minutes, (0.06 MPa-0.08 MPa)/30 minutes, (0.08 MPa-0.1 MPa)/30 minutes, total 6 hours; wherein the temperature elevated suddenly once to 50° C. The third operation is the same as the second operation, air at 31° C. was introduced into the heat treatment furnace, and the passivation was carried out for 6 hours. Fourth, the pressure was increased from 200 Pa to 0.1 MPa in 4 stages using air at 31° C.: (200 Pa-0.01 MPa)/30 minutes, (0.01 MPa-0.03 MPa)/30 minutes, (0.03 MPa-0.06 MPa)/30 minutes, (0.06 MPa-0.10 MPa)/30 minute, total 2 hours. The four passivations were carried out in total 21 hours. After the passivation, the tantalum powder was taken out, and generated heat seriously. The heat treated tantalum powder was passed through 80 mesh screening to obtain E-1h tantalum powder. The oxygen and hydrogen contents of the tantalum powder were analyzed, the results were shown in Table 1. 2 wt % magnesium powder based on the tantalum powder was blended to form a mixed powder, the mixed powder was charged into the tantalum powder deoxidization reaction vessel as shown in FIG. 5, held at 850° C. for 3 hours to carry out deoxidization treatment, the heating was stopped, and the temperature was lowered, and the treated tantalum powder was nitridated at 280° C., according to the passivation procedure similar to the heat treatment as described above, when the temperature was lowered to 31° C., air at 31° C. was introduced in 4 times to carry out passivation. The first 3 passivations were carried out in 8 stages for 5 hours each, and the fourth passivation was carried out in 4 stages for 2 hours, total 17 hours. The passivated tantalum powder was pickled, washed with water, and dried to obtain E-1d tantalum powder. The oxygen and hydrogen contents of the tantalum powder were analyzed, the results were shown in Table 1. The electric performance of the tantalum powder was determined, and the results were shown in Table 2.

TABLE 1 the oxygen and hydrogen contents of the tantalum powder tantalum powder No. O H S-1h 10600 70 S-1d 3800 140 S-2h 11300 78 S-2d 4100 140 S-3h 11600 60 S-3d 4000 130 E-1h 16500 180 E-1d 5800 200

TABLE 2 Measurement results of electric performance of tantalum powder tantalum powder Leakage current Specific capacity Loss No. nA/g μF · v/g (tg δ) % S-1d 58 85860 30.5 S-2d 59 85800 31.1 S-3d 59 84900 32.8 E-1d 126 85000 45.2

As seen from the results of Tables 1 and 2, the method of present invention has the advantages of short production period, and the tantalum powder prepared has low oxygen and hydrogen contents, and low leakage current.

Example 4

The tantalum powder S-1d in Example 1, after deoxidization heat treatment, was compacted into a cylindrical compact with a density of 4.5 g/cm³, a diameter of 3.0 mm and a height of 4.72 mm, in which 0.3 mm tantalum wire was embedded, each compact contained about 150 mg of tantalum powder; in a device as shown in FIG. 4, the compact was sintered at 1320° C. for 10 minutes to form a tantalum agglomerate, and then heating was stopped, the temperature was lowered to 200° C., argon was introduced, and the forced-cooling argon system 400A was actuated, the cooling was carried out for about 3 hours to lower the temperature in the furnace to 20° C., and the tantalum agglomerate was passivated. The passivation process comprises: evacuating the argon in the furnace to a vacuum of about 200 Pa; first, an oxygen-containing gas at −10° C. to −40° C. in a concentration of about 10 vol. % was introduced into the heat treatment furnace in 5 stages and 3 hours to increase the pressure in the furnace from 200 Pa to 0.1 MPa: (200 Pa-0.01 MPa)/40 minutes, (0.01 MPa-0.03 MPa)/40 minutes, (0.03 MPa-0.05 MPa)/40 minutes, (0.05 MPa-0.07 MPa)/30 minutes, (0.07 MPa-0.1 MPa)/30 minutes. Second, air at −10° C. to −40° C. was introduced into the heat treatment furnace in 4 stages and 2 hours to increase the pressure in the furnace from 200 Pa to 0.1 MPa: (200 Pa-0.01 MPa)/30 minutes, (0.01 MPa-0.03 MPa)/30 minutes, (0.03 MPa-0.06 MPa)/30 minutes, (0.06 MPa-0.10 MPa)/30 minutes. The two passivations were carried out in total 5 hours. During the whole procedure, the temperature in the furnace was firstly elevated gradually to 32° C., then the temperature was gradually steady and varied between 29° C. and 31° C., and finally the temperature was lowered gradually to 29° C. After discharging, the tantalum powder was taken out, and a tantalum agglomerate S-4 was obtained. The oxygen and hydrogen contents of the tantalum agglomerate were analyzed, the results were shown in Table 3. The agglomerate was placed in 0.1 mass % phosphoric acid at 80° C., the voltage was raised at current density of 60 mA/g to 30 V and maintained constant pressure for 120 minutes to form a tantalum anode S-4a; the leakage current of the anode was determined in 0.1 mass % phosphoric acid at 25° C., and the specific electric capacity (specific capacity) and loss were determined in 20 mass % of sulfuric acid solution, the results were shown in Table 4.

Comparative Example 2

The same tantalum powder as in Example 4 was compacted into same tantalum compact, and sintered under same condition, the temperature was lowered to 200° C., argon was introduced to cool for about 6 hours to lower the temperature in the furnace to 33° C., and tantalum agglomerate was passivated. The passivation process comprises: evacuating the argon in the furnace to a vacuum of about 200 Pa, first, air at 32° C. was introduced into the heat treatment furnace in 6 stages and 4.5 hours to increase the pressure in the furnace from 200 Pa to 0.1 MPa: (200 Pa-0.005 MPa)/60 minutes, (0.005 MPa-0.01 MPa)/30 minutes, (0.01 MPa-0.02 MPa)/30 minutes, (0.02 MPa-0.03 MPa)/30 minutes, (0.03 MPa-0.05 MPa)30 minutes, (0.05 MPa-0.06 MPa)/30 minutes, (0.06 MPa-0.08 MPa)/30 minutes, (0.08 MPa-0.1 MPa)/30 minutes. Second, air at 32° C. was introduced into the heat treatment furnace in 4 stages and 2 hours to increase the pressure in the furnace from 200 Pa to 0.1 MPa: (200 Pa-0.01 MPa)/30 minutes, (0.01 MPa-0.03 MPa)/30 minutes, (0.03 MPa-0.06 MPa)/30 minutes, (0.06 MPa-0.10 MPa)/30 minutes. The two passivations were carried out in total 6.5 hours. During the whole procedure, the temperature in the furnace was firstly elevated gradually to 41° C., After discharging, the tantalum agglomerate was taken out to obtain tantalum agglomerate E-2s. The oxygen and hydrogen contents of the tantalum agglomerate were analyzed, the results were shown in Table 3. The agglomerate was formed to an anode E-2a under the same condition as described in Example 3. The electric performance of the agglomerate was determined, and the results were shown in Table 4.

TABLE 3 the oxygen and hydrogen contents of the tantalum agglomerate tantalum agglomerate No. O H S-4 5200 30 E-2 6500 70

TABLE 4 Measurement results of electric performance of tantalum agglomerate tantalum powder Leakage current Specific capacity Loss No. nA/g μF · v/g (tg δ) % S-4 48 85800 30.1 E-2 93 84000 44.8

It was seen from above description that the heat treatment of tantalum powder by the inventive method is safe and reliable, has high yield, and tantalum powder does not burn, and the tantalum powder prepared has low oxygen and hydrogen contents, and the anode prepared from the tantalum powder has low leakage current and good electric performance.

In the above description, although the description is mainly directed to tantalum powder, a person skilled in the art can envisage that present invention is also suitable for other active metal powders, such as niobium powder. 

1. (canceled)
 2. A method for passivating tantalum metal surface, characterized in that it comprises following steps: a). providing tantalum metal which has been subjected to heat treatment; b). lowering the temperature of the tantalum metal to room temperature; c). introducing an oxygen-containing gas at 0° C. or below, preferably 0° C. to −40° C., to passivate tantalum metal surface; and d). optionally repeating the step c) once or more.
 3. A method for passivating tantalum metal surface, characterized in that it comprises following steps: a). providing tantalum metal which has been subjected to heat treatment; b). lowering the temperature of the tantalum metal to 32° C. or below, preferably below 30° C., and more preferably 10° C.-30° C., by using cooled inert gases; c). introducing an oxygen-containing gas at 0° C. or below, and preferably 0° C. to −40° C. to passivate tantalum metal surface; and d), optionally repeating the step c) once or more.
 4. A method of passivating tantalum metal surface according to claim 2, characterized in that the oxygen-containing gas is air, a mixture gas of inert gas and oxygen, or a mixture gas of inert gas and air.
 5. A method of passivating tantalum metal surface according to claim 2, characterized in that the oxygen-containing gas is air, a mixture gas of inert gas and oxygen, or a mixture gas of inert gas and air.
 6. A method of passivating tantalum metal surface according to claim 2, characterized in that the oxygen-containing gas is a mixture gas of argon and air.
 7. A method of passivating tantalum metal surface according to claim 2, characterized in that the concentration of oxygen in the oxygen-containing gas is 21 vol. % or below, preferably 5-20 vol. %.
 8. A method of passivating tantalum metal surface according to claim 3, characterized in that said inert gas is argon.
 9. An apparatus for carrying out the method of claim 1, the apparatus comprising a heat treatment furnace, the heat treatment furnace comprising: a hearth, a shell with a water-cooling jacket constituting the hearth, an inlet for the oxygen-containing passivation gas to enter the hearth, aeration pipelines, a heater arranged within the hearth, and a heat treatment crucible for accommodating tantalum metal to be treated; characterized in that the apparatus further comprises a refrigeration system for an oxygen-containing gas, the refrigeration system of an oxygen-containing gas comprising: an inlet of an oxygen-containing gas, which is used for receiving an oxygen-containing gas for passivating tantalum metal; a heat exchange chamber, the oxygen-containing gas is cooled in the heat exchange chamber by means of heat exchange; and an outlet of an oxygen-containing gas, the cooled oxygen-containing gas leaves the heat exchange chamber from the outlet and enters the heat treatment furnace from the upper part of the heat treatment furnace through thermal insulation connection pipelines.
 10. An apparatus for carrying out the method of claim 2, the apparatus comprising a hearth, a shell with a water-cooling jacket constituting the hearth, an inlet for oxygen-containing passivation gas entering the hearth, an inlet for argon entering into the hearth, an argon outlet positioned at upper part of the heat treatment furnace, a heater arranged within the hearth, and a heat treatment crucible for accommodating tantalum metal to be treated; characterized in that the apparatus further comprises an argon forced-cooling device and a refrigeration system of an oxygen-containing gas, wherein the argon forced-cooling device comprising: an inlet for argon to be cooled, the inlet for argon to be cooled being connected to the argon outlet at the upper part of the heat treatment furnace; a heat exchange chamber, the heat exchange chamber receives argon at a high temperature from the heat treatment furnace by means of the inlet for argon to be cooled and cools it by heat exchange manner; an outlet of cooled argon, the argon cooled in the heat exchange chamber being discharged from the outlet of argon; a circulating pump, the circulating pump receives the cooled argon from the outlet of cooled argon, and supplies the cooled argon into the heat treatment furnace from the inlet for argon at the lower part of the heat treatment furnace through connection pipelines; and wherein the refrigeration system of an oxygen-containing gas comprising: an inlet of an oxygen-containing gas, which is used for receiving an oxygen-containing gas for passivating tantalum metal; a heat exchange chamber, the oxygen-containing gas is cooled in the heat exchange chamber by means of heat exchange; and an outlet of an oxygen-containing gas, the cooled oxygen-containing gas leaves the heat exchange chamber from the outlet and enters into the heat treatment furnace from the upper part of the heat treatment furnace through thermal insulation connection pipelines.
 11. An apparatus for passivating tantalum metal surface according to claim 10, characterized in that the tantalum metal is cooled to 32° C. or below, preferably 10° C. to 30° C., by means of the argon forced-cooling device.
 12. An apparatus for passivating tantalum metal surface according to claim 10, characterized in that the refrigeration system of an oxygen-containing gas cools the oxygen-containing gas to provide an oxygen-containing gas for passivation at a temperature of 0° C. or below, preferably −40° C. to 0° C.
 13. An apparatus according to claim 11, characterized in that the refrigeration, system of an oxygen-containing gas cools the oxygen-containing gas to provide an oxygen-containing gas for passivation at a temperature of 0oC or below, preferably −40oC to 0oC 